Hi,
If it's for the competition, you cannot composite any output of other engines into your animation no...
If we allow this, the rules become too blurry and we won't be able to figure out what is octane and what not as a jury member.
I'm sure you can render particles with octane though, you could convert them to small triangulated mesh geometries and then use an emitting material or whatever suits...
This is the object of the competition, trying to achieve tasks that are not easy to do, and our technical achiement prize will definately be awarded to things like this.
Radiance